The present invention concerns a method of manufacturing a diffraction grating by light irradiation.
A diffraction grating is an optical device in which a plurality of grooves are engraved each at a period of a nm order, which is indispensable as a light source or a receiver for use in optical communication and, further, analyzers. As a base material of the diffraction grating requiring high accuracy, an inorganic material, particularly, glass is usually used. For manufacturing a diffraction grating on a glass substrate, a ruling engine is used and the grating is formed by engraving the grooves one by one. Such a manufacturing method is time consuming and requires a high production cost.
Accordingly, if the grooves of the diffraction grating can be formed by the irradiation of light, it is possible to remarkably shorten the time and reduce the cost. Under the situations as described above, it has been reported recently a method of irradiating an excimer laser beam to a thin GeO2xe2x80x94SiO2 glass film manufactured by sputtering through a phasemask and forming the diffraction grating in accordance with the period of the mask (Japanese Patent No. 2832337). The phase mask is used because the excimer laser beam has no sufficient coherency and no interference fringe can be formed by a usual two beam interference method. Such a method also involves a problem that a pulse light at several tens mJ/cm2 has to be irradiated for several thousands of times for forming.
For overcoming the foregoing problems, it may be considered a method of forming by using an interference light at a lower energy with a large coherent length such as an Hexe2x80x94Cd laser or argon ion laser. However, since the thin film formed by the sputtering has low light sensitivity, formation of the diffraction grating is difficult by the interference light at low energy. Accordingly, it has been demanded for the development of a light responsive material of higher sensitivity as a material for the manufacture of a diffraction grating. It has also been demanded for the development of a so-called blazing technique of making the shape of the grating asymmetric in order to improve the diffraction efficiency of the diffraction grating.
This invention intends to provide a method of manufacturing a diffraction grating capable of forming by an interference light at a lower power density than usual.
The present inventor has found that the foregoing object can be attained by coating a solution containing a metal alkoxide and a xcex2-diketone on a substrate, applying a heat treatment to form a gelled film and irradiating an interference light to the gelled film, and has accomplished this invention.
That is, a method of manufacturing a diffraction grating according to this invention comprises coating a solution containing a metal alkoxide and a xcex2-diketone on a substrate, applying a heat treatment to the coated film to form a gelled film and then irradiating an interference light to the gelled film.
The metal of the metal alkoxide can be, for example, one of zirconium, aluminum or titanium.
The xcex2-diketone can be, for example, any one of benzoyl acetone or acetyl acetone.
The solvent for the coating solution can be a mixed solvent of water and an alcohol.
The alcohol can be at least one alcohol selected from the group consisting of methanol, ethanol and isopropyl alcohol.
The blending ratio for each of the ingredients, by molar ratio, in the coating solution is defined as:
0.5xe2x89xa6metal alkoxide/xcex2-diketonexe2x89xa63, and
0.01xe2x89xa6(metal alkoxide+xcex2-diketone)/solventxe2x89xa62
The coating solution can contain zirconium tetrabutoxide (Zr(O-nBu)4), benzoyl acetone (BzAcH), ethanol (EtOH) and water (H2O), in which the blending ratio of them, by molar ratio, is defined as:
0.5xe2x89xa6Zr(O-nBu)4/BzAcHxe2x89xa61.5,
0.1xe2x89xa6H2O/EtOHxe2x89xa60.2, and
0.01xe2x89xa6(Zr(O-nBu)4+BzAcH)/(EtOH+H2O)xe2x89xa60.4.
The coating solution can contain aluminum tri-sec-butoxide (Al(O-sec-Bu)3), benzoyl acetone (BzAcH), and isopropyl alcohol (i-PrOH), in which the blending ratio of them, by molar ratio, is as defined as:
0.5xe2x89xa6Al(O-sec-Bu)3/BzAcHxe2x89xa63, and
0.01xe2x89xa6Al(O-sec Bu)3+BzAcH)/(i-PrOH)xe2x89xa62.
The coating solution can contain titanium tetrabutoxide (Ti(O-nBu)4), benzoyl acetone (BzAcH), methanol (MeOH) and water (H2O), in which the blending ratio of them, by molar ratio, is defined as:
0.5xe2x89xa6Ti(O-nBu)4/BzAcHxe2x89xa62.5,
0.01xe2x89xa6H2O/MeOHxe2x89xa60.2, and
0.01xe2x89xa6(Ti(O-nBu)4+BzAcH)/(MeOH+H2O)xe2x89xa61.
The heat treatment can be applied in atmospheric air at 50 to 150xc2x0 C. for 1 min to 2 hours.
The light source for the interference light can be an Hexe2x80x94Cd laser or an argon ion laser and an average power density for the interference light is preferably from 0.5 to 100 mW/cm2.
After the irradiation of the interference light, the irradiated surface is preferably cleaned with a solvent.
For the solvent, an organic solvent, particularly, an alcohol is used preferably.
After cleaning, a pressurized gas is preferably blown to the light irradiated surface.
It is preferred that the blowing direction of the pressurized gas is in perpendicular to the grooves of the diffraction grating, at an angle of 5 to 80xc2x0 relative to the substrate and the blowing pressure is from 0.5 to 5 atm.
After the cleaning, a heat treatment is preferably applied at a temperature from 50 to 500xc2x0 C. for 1 min to 5 hours.